Overall thoughts:
This book covers a *lot* of ground. All core and base classes through the "Ultimate" books are present along with another 11 from various third party publishers
Hyperlinked. I've not needed to use them, but anything that immediately brings up its reference is a good thing. As I recall, these link to the d20pfsrd pages.
Some typos. There are no horrendous issues on this front, but there were a few that stood out to me (p. 77, Mythic Scribe Scroll asks me to reference page XX, references to DR x/epic [which may be a mistake on my part]).
Mythic Misc. Chapter. This itself may be the selling point of the books, offering substantive re-workings of some perceived problems with the Mythic tool set along with a Mythic Skill system.
Mythic Versions of Class Abilities. This is another excellent innovation to the Mythic concept: Why not have a character of myth be amazing at a signature ability, such as the Rage of Achilles?
Expanded Mythic Paths. I'm partial to the Psionic Path (The Overmind, and the Carrie-like abilities) there seems to be nothing lacking or ridiculously off in any of the included new paths.
Feats. No, I'm talking something more FEATS. It seems like every feat in the PF hardbound line is in this book.
Finally, something I wouldn't hold against any publisher: no love for Words of Power.
Closing words: Awesome book. I would need to play the paths and abilities/feats some to get a better feel of the overall balance, but I am immensely happy with this text. I imagine any perceived issues are balanced by the other two books in this "series," and look forward sitting down with them eventually.